As a damping valve, there has been a variable damping valve that makes a damping force of a shock absorber, which is interposed between a vehicle body and axle shafts in a vehicle, variable. As this damping valve, for example, the applicant of the present application has been proposed a damping valve that includes a valve seat member, a main valve element, a pilot passage, an orifice, a spool, a valve housing, a pilot valve, and a solenoid. The valve seat member includes a port passing through from a cylinder to a reservoir and an annular valve seat surrounding the port. The main valve element is laminated on the valve seat member, and is seated on and separated from the annular valve seat to open and close the port. The pilot passage is branched from the upstream of the port. The orifice is disposed on the middle of the pilot passage. The spool has a tubular shape, and is in contact with the opposite side of the annular valve seat of the main valve element. The valve housing includes the spool slidably mounted on the outer periphery of the valve housing, and forms a back pressure chamber on the back side of the main valve element with the spool. The pilot valve is disposed on the downstream of the pilot passage. The solenoid adjusts a valve opening pressure of the pilot valve. This damping valve guides a secondary pressure that is downstream of the orifice in the pilot passage into the back pressure chamber to cause the secondary pressure to press the main valve element.
In this damping valve, the pilot valve is disposed on the downstream of the back pressure chamber. Then, adjusting the valve opening pressure of the pilot valve by a thrust of the solenoid controls the secondary pressure guided into the back pressure chamber to functions as the valve opening pressure of the pilot valve.
On the back surface of the main valve element, the secondary pressure acts to press the main valve element on the annular valve seat side. On the front of the main valve element, a pressure to separate the main valve element from the annular valve seat acts from the upstream of the port. Accordingly, the damping valve opens when a force to separate the main valve element from the annular valve seat by the pressure on the upstream side of the port exceeds a force to press the main valve element on the valve seat by the secondary pressure.
That is, controlling the secondary pressure ensures the valve opening pressure of the damping valve to be adjusted. Adjusting the valve opening pressure of the pilot valve by the solenoid ensures a resistance provided to a flow of hydraulic oil passing through the passage by the damping valve to be variable. This causes the shock absorber to generate a desired damping force.